The present invention relates to a method of foreseeing and/or controlling tread wear in a pneumatic tire and a related pneumatic tire suitably arranged for use of such a verification method. More particularly, the invention relates to a method of foreseeing and/or controlling tread wear in a tire while leaving substantially unchanged the integrity of the tire.
It is known that a pneumatic tire generally consists of a carcass of toric form, having a crown on which is a disposed tread band of elastomeric material constituting the ground-contacting portion of the tire running on a road. The tread band is generally comprised of a raised pattern mainly consisting of a plurality of land portions in the form of ribs and/or blocks distributed according to various configurations, defined and separated from each other by a plurality of grooves directed longitudinally and/or transversely of the tire, the depth of said grooves defining the height of said land portions.
It is known that during tire use the tread is subjected to wear, which wear can be classified according to two distinct types, that is one of (a) an uneven type identified by the appearance of localized early wear marks at some particular areas, the land edges for example where abrasion is more pronounced than at other areas, and (b) one of an even type that goes on at a given velocity until the complete disappearance of the tread pattern. Uneven wearing is particularly dangerous because it greatly affects the tire behavior on driving, giving rise to vibrations and difficulties in keeping the desired path; in addition, since this wearing reveals itself in the form of localized spots even of great width, it can involve extra costs due to the impossibility of using a tire which, taking into account the remaining tread portion, could otherwise still be used, since the residual height of the pattern lands are still prominent.
Even wearing affects the tire behavior on the road to a lesser degree and in particular its effect consists of progressively reducing the tire features in terms of traction capability and resistance to aquaplaning, but the rate at which it takes place is an essential qualitative element in judging a tire, since a slow rate of wear corresponds to a long duration of the tire, which is a desired requirement.
On planning a new tire as well as on carrying out quality control of an existing tire, it is therefore of the greatest importance to verify the type and rate of wearing of the tread band. The verification method mainly used at the present time consists in making a vehicle, provided with test tires, driving over a given road circuit, bringing the tire to its complete wearing or in any event until an important reduction in the tread band thickness occurs; in this manner it is possible to progressively evaluate, by means of inspections at subsequent times, whether the tire wearing is of an even or uneven type and, at the end of the service life of the tire, the rate of wear of the tread. Unfortunately, for this type of test very long execution times are required in that only abrasions of some importance can be seen with the naked eye and can be measured using the present measurement means and methods which substantially enable wear to be measured through the measurement of the decreased depth of the grooves and the loss of weight suffered by the tire. Therefore, the above are very demanding and expensive tests, due to the fact that it is necessary to make use of several persons and related vehicles over a long period of time; in this connection, it is important to remember that evaluations are always made by comparison with sample tires.
For example, the tread of a tire may come to the end of its service life after it has covered a distance of about 50,000 km in the case of usual car tires and a distance as high as 150,000 km in the case of heavy duty tires. Practically, if in a very simple manner a distance of 1,000 km per day is assumed to be covered, the conclusion is that for each type of tire to be tested a person and a test means need to be used over a period of time varying from two to five months.
As an alternative solution to road tests, attempts have been made to standardize the so-called "indoor" wear tests, that is tests performed in the laboratory, in workshops or in any case in suitably equipped premises, where the tire is set in rotation against a wheel of a much bigger diameter than that of the tire and covered with a layer of material having predetermined abrasive features. However, as well known to those skilled in the art, the results of indoor tests can be scarcely correlated with those of road tests; in particular, they greatly depend on the selected abrasive layer and the test modalities, and the abrasion layer features and test conditions do not always succeed in correctly simulating the abrasions caused to the tire during the actual road use. In conclusion, said indoor tests are sometimes trustworthy but sometimes not very reliable, so that they substantially do not seem to have the capability of foreseeing the actual behavior of the tire in use.